LAARS Rheos+ RHHV - Install and Operating Manual - Manual (Page 26)

Rheos+ Boiler and Water Heater Page 25
temperature is less than 140°F (60°C), internal mixing
will keep the outlet temperature at 160-165°F (71-
74°C), and this will mix with the tank temperature
to maintain a lower temperature in the tank. If the
return temperature is 140°F (60°C) or higher, the
outlet temperature of the heater will be the return
temperature plus 20-25°F (11-14°C) when the Rheos+
is at high firing rate.
The manual reset high limit is on the outlet of
the Rheos+. Set the manual reset high limit at about
20°F (11°C) higher than the highest expected outlet
temperature, to avoid nuisance lockouts
5.4.2 Internal Water Heater
Temperature Control
When an external control is not used, the
circulator between the heater and the storage
tank must run continuously, so that the heater’s
temperature control can detect and control the water
temperature in the storage tank. The Rheos+ water
heater’s temperature control is adjusted to its lowest
temperature position when shipped from the factory.
This is the preferred starting point for setting the
temperature control.
The Rheos+ temperature control measures
temperature on the heater inlet, sensing return water
temperature. If the return water temperature is less
than 140°F (60°C), internal mixing will keep the outlet
temperature at 160-165°F (71-74°C), and this will
mix with the tank temperature to maintain a lower
temperature in the tank. If the return temperature is
140°F (60°C) or higher, the outlet temperature of the
heater will be the return temperature plus 20-25°F (11-
14°C) when the Rheos+ is at high firing rate.
The manual reset high limit is on the outlet of
the Rheos+. Set the manual reset high limit at about
20°F (11°C) higher than the highest expected outlet
temperature, to avoid nuisance lockouts.
Caution
Should overheating occur or the gas supply fail to
shut off, turn off the manual gas control valve to the
appliance.
5.5 Temperature Control Features
The Rheos+ temperature control is versatile and
will allow the user to better match the modulating
control to the application. Settings that can be changed
are temperature setpoint, differential, offset, throttling
range, and minimum output.
The temperature setpoint is the setting at which
the unit will shut off, having satisfied the controller’s
call for heat.
The differential determines how far the
temperature in the Rheos+ can fall before
energizing again.
The offset determines where the throttling range
begins.
The throttling range is the temperature range
through which the unit will modulate from minimum
to maximum firing rate.
Important Note: These control parameters work
together. Therefore, setting one parameter may have
an affect on another. Figures 14, 15 and 16 show the
relationships between these settings. Figure 14 follows
the examples that are shown in the following sections,
and Figures 15 and 16 are examples of how the
parameters can interfere with each other.
5.5.1 Temperature Setpoint
The temperature setpoint is the point at which the
temperature control relay will be de-energized and the
unit’s call for heat will end. The temperature setpoint
is adjusted with the setpoint dial on the A350 control
(see Figure 13). The temperature control’s sensor is in
the inlet of the unit.
V C I
Cover Screws
(Quantity=4)
Integration
DIP Switch
is set to
“Medium” at
the factory.
See Section
5.5.6 for
descriptions
of other
settings.
LED Indicator
(Percent of
Output)
Module
Connector
THROT
RANGE
MIN
OUTPUT
OFFSET
Reverse
Acting
Direct
Acting
Operation Mode
Jumper Positions
Figure 13 - Proportional Control
Note: Jumper must be in “Reverse Acting” mode, or Rheos will not
operate properly.
5.5.2 Differential Setting
The differential is the difference in temperature
settings when the temperature control’s relay is
energized and de-energized. For instance, if the
temperature setpoint is 120°F (49°C) and the
differential is 20°F (11°C), the temperature control
will call the unit to energize at 100°F (38°C). (The
differential is the setpoint minus the differential
setting) The call for heat will end when the unit
reaches its setpoint of 120°F (49°C). The Rheos+
differential is adjustable from 1°F to 30°F (1°C to
17°C). In general, the differential setting for a water
heater system will be low, so that when a storage tank